14

Ventilation

2

Objectives• Define ventilation as it relates to fire suppression activities.• List the effects of properly performed ventilation on fire and fire

suppression activities.• Describe how fire behavior principles affect ventilation.• Describe how building construction features within a structure affect

ventilation.• Define horizontal and vertical ventilation.• List the principles, advantages, limitations, and effects of

horizontal/vertical/mechanical/natural ventilation. • List the principles, advantages, limitations, and effects of positive-

pressure, negative-pressure and hydraulic ventilation.• List safety precautions for ventilating roofs.• List the basic indicators of roof collapse.• Explain the role of ventilation in the prevention of backdraft and

flashover.

14

3

Introduction

• Primary method of fire spread is convection

• Mushrooming occurs when the products of combustion reach the highest point.

• Products of combustion present a risk to fire fighters and occupants.

14

• Ventilation – The process of removing smoke, heat, and toxic gases from

a burning building and replacing them with cooler, cleaner, more oxygen-rich air

4

Benefits of Proper Ventilation • Locate trapped occupants faster• Fresh air to occupants overcome by smoke• Advance hose lines more rapidly and safely• Reduce backdraft and flashover• Limits fire spread• Reduces property loss

14

Vented structureUnvented structure

5

Factors Affecting Ventilation

• Wind and atmospheric forces– Wind speed and direction

– Temperature and humidity

14

• Convection currents• Mechanical ventilation activities

– Negative-pressure

– Positive-pressure

– Hose streams

6

Fire-Resistive Construction

• Construction design - Structural components noncombustible- Compartmentalization

• Paths of fire spread– Heating, Ventilation, and Air Conditioning– Stairways– Elevator shafts

• Roofs generally of steel or concrete

14

Building Construction• The way a building is constructed will affect ventilation operations.

7

Ordinary Construction

• Construction design– Exterior walls noncombustible

– Interior walls/floors of wood

– Roof is wood decking and structural support

• Paths of fire spread– Plumbing and electrical chases

– Void spaces in walls

– Cockloft

14

Wood-Frame Construction

• Construction design– Similar to ordinary but

exterior walls are combustible

• Paths of fire spread– Attics and cocklofts

– Wood truss roofs and floors

• Construction types– Balloon-frame

– Platform

8

Ventilation and Tactical Priorities• Ventilation is directly related to tactical priorities.

14

Venting for Life Safety• Life safety is the primary goal.

• Gives occupants a greater chance to survive

• Makes searches faster

• Limits fire spread to other occupants and fire fighters

Venting for Confinement

• Second highest priority is contain the fire and control the situation

• Prevents fire spread

• Makes fire attacks easier

Venting for Property Conservation

• Limits amount of damaged areas

• Rapid removal limits amount of permanent damage.

9

Location and Extent of Smoke and Fire Conditions• Factors to consider

– Size of the fire

– Stage of combustion

– Location within the building

– Available ventilation options• Determine fire size, intensity, and fuel

– Light smoke, moving lazily—small fire of ordinary combustibles

– Large amount of black rolling smoke—petroleum base fire

– Hotter the fire, the faster the smoke moves

– Cool days may cause smoke inversion.

– Sprinkler activation may cause the smoke to cool and act as a fog.

14

• Where to ventilate– As close to the fire as

possible• Directly over the seat• Through an open door or

window that opens outside

– If unable to vent close to the fire

• Predict how location will affect the fire

• Anticipate fire spread and locate hose lines for protection

10

Types of Ventilation

• Two basic types of ventilation– Horizontal

• Utilizes horizontal openings in a structure such as doors and windows

– Vertical • Involves openings in the roofs or floors

14

11

Horizontal Ventilation• Commonly used in

– Residential fires

– Room-and-contents fires

– Fires that can quickly be controlled

• Generally fast and easy to use• Can be used from inside or outside the

building• Most effective when opening is directly to

outside• More difficult when there are no

openings• Limits structural damage• May utilize natural and mechanical

methods

14

12

Methods of Ventilation

• Natural– Depends on convection currents, wind, and other

natural air movement– Used when air currents are adequate– Used when ventilation is needed quickly– Open leeward side of building first, then windward.

• Mechanical– Uses mechanical means to augment natural

ventilation

14

13

Breaking Glass

• General rules– Try to open first.– Wear full protective

clothing and eye protection.

– Ensure no one will be struck by the glass.

– Always use a tool.– Keep hands above or to

the side of the glass.– Use a tool to clear

remaining glass.

14

14

Opening Doors

• Provide large openings

• May compromise entry/exit points

• May be best for fresh air points

• Good location for mechanical ventilation devices

14

15

Mechanical Ventilation

• Methods of Mechanical Ventilation– Negative-pressure– Positive-pressure– Hydraulic

14

16

Negative-Pressure Ventilation

• Uses fans called ejectors to exhaust smoke and heat

• Limitations:– Positioning– Power source– Maintenance– Air flow control

• Advantages– Explosion-proof motors

14

17

Positive-Pressure Ventilation

• Uses large, powerful fans to force fresh air into a structure.

• Advantages:– Quick and efficient– Increased safety

• Disadvantages– May spread the fire– May increase carbon

monoxide levels

14

18

Hydraulic Ventilation

• Uses a fog or broken pattern stream to create a pressure differential

• Advantages– Can move several

thousand cubic feet of air per minute

– Does not require specialized equipment

• Disadvantages– Water damage– Safety hazards

14

19

Vertical Ventilation• Releases combustion

products vertically• Occurs naturally if there

is an opening• May be assisted by

mechanical means• Usually involves making

openings in roof• Make opening close to

seat of fire• Determine hottest point

14

20

Safety Considerations

• Structural stability of the roof• Falling from the roof• Two exit routes• Not getting opening between you and the exit• Have a charged hose line• Leave the area once done• “Sound” the roof• Walk on areas of greatest support• Make cuts from

– Upwind

– With clear exit path

– While standing on firm section

14

21

Basic Indicators of Roof Collapse

• Spongy feeling

• Visible sagging

• Roof separating from the walls

• Structural failure in another portion of building

• Sudden increase in fire intensity

14

22

Roof Construction

• Two components– Support structure

• Solid beams of wood, steel, or concrete• System of trusses of wood, steel, or wood and

steel

– Roof covering• Made of various water repellant materials• Supported by the roof decking

14

23

Types of Roof Failures

• Support system failure– Supporting structure fails– Often a sudden and total collapse– Areas with heavy snow loads more prone

• Roof covering failure– Burns through roof covering close to seat of fire– Spreads out causing roof failure– Areas with light snow loads more prone

14

24

Solid Beam vs. Truss

• May not be able to tell by looking

• Solid beam– Girders, beams, and

rafters

• Truss– Lightweight components,

often 2" x 4" wood with gussets or staples

– Steel bars welded together

– Triangular configuration

14

25

Roof Designs• Flat roofs

– Can be constructed with many types of supports, decking, and materials

• Pitched roofs– Have a visible slope for rain, ice,

and snow runoff

• Arched roofs– Generally found in commercial

structures to create a large span without columns

14

26

Objectives of Vertical Ventilation

• Provide the largest opening

• Put in an appropriate location

• Use the least amount of time

• Use the safest technique

14

27

Vertical Ventilation Assessment

• Construction features• Indications of fire damage• Safety zones and exit paths• Built-in roof openings• Locate at highest point and over seat of fire• May need to cut an examination hole• One hole is better than several small ones• Minimum size 4' x 4'

14

28

Tools Used in Vertical Ventilation

• Power saws

• Axes

• Halligans

• Pry bars

• Tin cutters

• Pike poles and other types of hooks

• Utility rope

14

29

Types of Roof Cuts

• Rectangular cut • Louver cut• Triangle cut• Peak cut• Trench cut

14

30

Rectangular or Square Roof Cut

• Requires four cuts completely through the decking

• Use care to not cut structural supports.

• Stand upwind and have a safe exit.

• Can use a triangle cut to help pry up

• If several layers exist, may have to peel a layer at a time

14

31

Louver Roof Cut

• Used for flat or sloping roofs with plywood decking

• Power saw or axe used to make the cuts

• Can quickly create a large opening

14

32

Triangle Roof Cut

• Used to prevent metal decking from rolling away as it is cut

• A saw or axe is used.

• Several may be needed because of their small size.

14

33

Peak Roof Cut

• Used for peaked roofs with plywood sheeting

• A tool is used to reveal the roof covering along the peak.

• A power saw or axe is used to make a series of vertical cuts between the supports.

14

34

Trench Roof Cut

• Used as a defensive tactic to stop the progress of a large fire in a narrow building

• Creates a large opening ahead of the fire

• “Writes off” part of the building• Requires both time and manpower

14

35

Special Considerations

• Obstacles preventing ventilation

• Concrete roofs

• Metal roofs

• Basement fires

• High-rise buildings

• Windowless buildings

• Large buildings

14

36

Obstacles to Ventilation

• Poor access• Multiple roofs and roof layers• Sealed and boarded abandoned

buildings• Security measures such as steel bars

and shutters• Concrete roofs• Metal roofs

14

37

Ventilating a Concrete Roof

• Found in commercial and industrial structures

• Generally flat and hard to breach

• May collapse from weakened support systems when exposed to fire

• Search for alternative openings

14

38

Ventilating a Metal Roof

• Discoloration and warping may indicate seat of fire.

• As fire heats the metal deck, tar roof covering can melt and leak into the building.

• Metal can roll down and create a dangerous slide directly into the opening.

14

39

Venting a Basement

• Usually few windows• Fire will quickly spread• Usually requires both horizontal and vertical

ventilation• Fire fighters must descend the stairs through

the venting combustion products.• Make as many openings on one side and

allow fire fighters to enter from the other

14

40

High-Rise Buildings

• Many have hard to break sealed windows. • They create unique smoke patterns with the

stack effect.• Newer buildings have smoke management in

the HVAC.• Designate one stairwell as a rescue route.• Positive-pressure fans can keep smoke out of

the stairs.

14

41

Stack Effect Smoke Patterns

14

42

Windowless Buildings

• Traps heat and smoke with no secondary exit

• Treat similar to a basement fire.

• Ventilate high and use mechanical assistance.

• May need to – use existing roof

openings, cut new ones– reopen boarded

windows/doors or make new openings

14

43

Large Buildings

• More difficult than small ones

• Smoke cools as it travels, causing stratification.

• When possible, use interior walls and doors to create smaller areas.

14

44

Backdraft

• May occur when building is charged with hot gases and most of oxygen has been consumed

• When air is introduced, fuel can ignite and explode.

• Prevent by releasing heat and unburned particles without allowing fresh air

• Ventilate as high as possible.• Once flaming begins, fire fighters may enter.

14

45

Flashover

• Needs both ventilation and cooling• Occurs when

– air in room is very hot and– all combustibles in the space are near their

ignition point

• Applying water cools the atmosphere• Ventilation draws the heat and flames

away

14

46

Summary (1 of 2)

• Ventilation provides many benefits.• Several factors affect ventilation.• Building construction affects ventilation

operations.• Ventilation is related to life safety, fire

containment, and property conservation.• Assessing the location and extent of smoke

and fire will determine ventilation operations.• The types of ventilation are horizontal and

vertical.

14

47

Summary (2 of 2)

• Horizontal ventilation uses horizontal openings in a structure.

• Vertical ventilation refers to the release of heat and smoke in a vertical direction.

• Many obstacles can be encountered during ventilation operations.

• Ventilation is a major consideration in backdraft and flashover.

14